Pre-polymerized catalyst components for the polymerization of olefins

ABSTRACT

Components of catalysts for the polymerization of olefins are obtained by contacting a Ti compound of formula Ti(OR)n-yXy, where n is the valence of titanium and y is a number between 1 and n, with a pre-polymer having a porosity higher than 0.3 cc/g and containing from 0.5 to 100 g of polymer per g of solid catalyst component, the pre-polymer being obtained by (co)polymerizing an olefin or a diolefin in the presence of a catalyst comprising a Ti, V, Zr of Hf compound supported on an Mg dihalide having a mean crystallite dimension lower than 30 nm.

The present invention relates to components of catalysts for thepolymerization of olefins CH₂═CHR, wherein R is hydrogen or ahydrocarbon radical having 1-12 carbon atoms. the catalysts obtainedtherefrom and their use in the polymerization of said olefins.

In particular, the catalyst components of the present invention are verysuitable for the preparation of crystalline propylene (co)polymers byusing gas-phase, slurry or bulk (co)polymerization processes.

Components of high-yield catalysts for the polymerization of olefins,and in particular for propylene, are known in the art. They aregenerally obtained by supporting, on a magnesium dihalide, a titaniumcompound and an electron donor compound as a selectivity control agent.Said catalyst components are then used together with an aluminum alkyland, optionally, another electron donor (external) compound in thestereospecific polymerization of propylene. Depending on the type ofelectron donor used the stereoregularity of the polymer can vary.However, the stereospecific catalysts of interest should be able to givepolypropylene (co)polymers having isotactic index, expressed in terms ofxylene insolubility, of higher than 90%.

Said catalyst components, and the catalysts obtained therefrom, arelargely used in the plants for the (co)polymerization of propylene bothoperating in liquid phase (slurry or bulk) and in gas-phase. However.the use of the catalyst components as such is not completelysatisfactory. Indeed, problems such as formation of polymers withirregular morphology and in particular of fines and low bulk density areexperienced when plants operate with catalyst components as such.

In order to solve these problems, the catalyst components are oftenpre-polymerized under controlled conditions, so as to obtainpre-polymerized catalysts having good morphology. Afterpre-polymerization, the catalysts also increase their resistance in sucha way that the tendency to break under polymerization conditions isdecreased. As a consequence, the formation of fines is reduced and themain polymerization process, either in slurry or gas-phase, can becarried out smoothly and with the production of final polymers havinghigh bulk density.

However, one of the possible drawbacks associated with this method isthe lowering of the activity expressed as amount of polymer obtained perg of catalyst fed. In other words. even if the activity of the catalystin itself (expressed in respect of the magnesium chloride contained inthe catalyst) could remain at the same level, the activity in respect ofthe pre-polymer/catalyst system, is lower due to the effect of thedilution of the catalyst within the pre-polymer. Depending on the degreeof pre-polymerization, the loss in activity can also be substantial.This means that a large amount of pre-polymer/catalyst system must befed to the reactor in order to obtain acceptable yields. It would betherefore important to have a pre-polymerized catalyst component inwhich this drawback is absent or minimized.

In the international patent application WO95/26369 the pre-polymerobtained by pre-polymerization of a catalyst component comprising a Ticompound supported on magnesium dihalide. is contacted with ametallocene compound in particular selected from the class ofzirconocenes. The resulting catalyst shows a good activity with respectto magnesium chloride therein contained but the yield is rather low ifreferred to the pre-polymer/catalyst system. In any case, the catalystobtained after treatment with the metallocene compound is different innature from the original conventional Ziegler-Natta catalyst so thatalso the polymers obtained show the typical features associated with theuse of metallocene catalysts such as a very narrow Molecular WeightDistribution. As a consequence, the polymerization results showed in theabove-cited patent application do not provide any useful teaching aboutthe possible activity of the original catalyst system contained in thepre-polymer.

The European patent application EP-A-604401 proposes the solution ofpre-polymerizing a catalyst component, comprising a titanium compoundand an electron donor compound supported on a magnesium dihalide, firstwith a linear olefin and then with a non linear olefin in order toproduce a linear olefin/non linear olefin copolymer as a pre-polymer.The so obtained pre-polymer/catalyst system is further contacted with aTi compound, in particular TiCl₄, and optionally also with an electrondonor compound in order to obtain a final catalyst component. Thepre-polymer/catalyst system obtained however, does not solve the problembecause the decrease of the activity observed in the polymerizationexamples if the activity is calculated as Kg of polymer produced per gof pre-polymer/catalyst fed, is always proportional to the dilution ofthe catalyst component in the pre-polymer. In other words, when theamount of pre-polymer is about 50% of the total pre-polymer/catalystsystem (see Table 2 of EP604401), the activity in the polymerizationtest is about a half of the activity of the non pre-polymerizedcatalyst. This means that, according to the disclosure of EP604401, thepre-polymerization step and the further titanation treatment did notimprove the activity of the catalyst in itself.

It has now unexpectedly been found a catalyst component having improvedactivity which is the product obtained by contacting a Ti compound offormula Ti(OR)_(n−y)X_(y), where R is an alkyl, isoalkyl, cycloalkyl oraryl radical having from 1 to 18 carbon atoms, preferably an alkyl,isoalkyl or cycloalkyl radical having from 1 to 8 carbon atoms. morepreferably n-butyl or isopropyl, X is a halogen atom, preferably achlorine or bromine atom, n is the valence of titanium and y is a numberof from 1 to n, with a pre-polymer having a porosity (measured with Hgmethod) higher than 0.3 cc/g and containing from 0.5 to 100 g of polymerper g of solid catalyst component, said pre-polymer being obtained by(co)polymerizing an olefin or a diolefin which is (co)polymerizable inthe presence of a catalyst comprising a solid component comprising atransition metal compound selected from the group consisting of Ticompounds of the above formula Ti(OR)_(n−y)X_(y), vanadium halides,haloalcoholates and vanadyl halides, Ti, Zr and Hf compounds containingat least a π-metal bond, said transition metal compound being supportedon a Mg dihalide having a mean crystallite size lower than 30 nm.

The porosity of the pre-polymer is preferably higher than 0.4 cc/g andstill more preferably higher than 0.5 cc/g. In the present applicationthe term (Hg) porosity referred to the pre-polymer means the porositymeasured by the mercury porosimetry method described below and due topores with radius up to 75,000 Å.

The amount of pre-polymer ranges preferably from 1 to 50 and preferablyfrom 2 to 30 g of polymer per g of solid catalyst component used toprepare it.

The term “pre-polymer” used hereabove and hereinafter means a polymerprepared under conditions such as to have a weight ratio polymer/solidcatalyst component equal to, or lower than 100; the catalyst used toprepare the pre-polymer being capable to give, under the propylene orethylene general polymerization conditions given below, a yield higherthan 1 Kg/g solid catalyst component.

The magnesium halides, preferably MgCl₂, in active form used as asupport for Ziegler-Natta catalysts, are well known. The activemagnesium halides are those having a mean crystallite size, determinedby X-ray diffractometry, lower than 30 nm and particularly preferred arethose in which the mean crystallite size is lower than 15 nm.Particularly preferred magnesium chlorides are those characterized byX-ray spectra in which the most intense diffraction line that appears inthe spectrum of the non-active chloride is diminished in intensity andis replaced by a halo whose maximum intensity is shifted towards lowerangles relative to that of the more intense line.

The preparation of the solid catalyst component used to prepare thepre-polymer can be carried out according to several methods. Preferredmethods are those producing catalyst components which, due to theirparticular physical properties are able to directly produce porouspre-polymers during the pre-polymerization step. In one of the preferredmethods the solid catalyst component is prepared by reacting a titaniumcompound of the general formula Ti(OR)_(n−y)X_(y) as above specified,preferably TiCl₄, with an adduct of formula MgCl₂.pROH, where p is anumber of from 0.1 to 6 and R is a hydrocarbon radical, suitably analkyl, isoalkyl or cycloalkyl radical, having from 1 to 18, preferablyfrom 1 to 8, more preferably from 1 to 4, carbon atoms. The adduct canbe suitably prepared in spherical form by mixing an alcohol of the aboveformula ROH and magnesium chloride in the presence of an inerthydrocarbon immiscible with the adduct, operating under stirringconditions at the melting temperature of the adduct. Then, the emulsionis quickly quenched, thereby causing the solidification of the adduct inform of spherical particles. Examples of spherical adducts preparedaccording to this procedure are described in U.S. Pat. Nos. 4,399,054and 4,469,648. The so obtained adduct can be directly reacted with theTi compound or it can be previously subjected to thermal controlleddealcoholation (80-130° C.) so as to obtain an adduct in which thenumber of moles of alcohol is generally lower than 3 preferably between0.1 and 2.5. The reaction with the Ti compound can be carried out forexample by suspending the adduct (dealcoholated or as such) in coldTiCl₄ (generally 0° C.); the mixture is heated up to 80-130° C. and keptat this temperature for 0.5-2 hours. The treatment with TiCl₄ can becarried out one or more times. When a stereospecific catalyst is to beprepared, an internal electron donor compound is added during thetreatment with TiCl₄. The treatment with the electron donor compound canbe repeated one or more times.

The preparation of catalyst components in spherical form according tothe above general procedure is described for example in U.S. Pat. No.4,399,054, EP-A-395083, EP-A-553805, WO98/44001.

According to another embodiment, the MgCl₂.pROH adduct is firstthermally dealcoholated according the procedure described above andsuccessively contacted with reactive compounds capable of removing thealcohol. Suitable reactive compounds are, for example, Al-alkylcompounds or SiCl₄. The so obtained adduct is then reacted with atitanium compound in order to obtain the final solid catalyst component.The preparation of catalyst components in spherical form according tothis procedure is described for example in EP-A-553806, and EP-A-601525.

In general, the solid catalyst components obtained according to themethods described above show a surface area (by B.E.T. method) between20 and 500 m²/g and preferably between 50 and 400 m²/g, and morepreferably between 100 and 400 m²/g; a total porosity (by B.E.T. method)higher than 0.2 cm³/g preferably between 0.2. and 0.6 cm³/g and morepreferably from 0.3 to 0.5 cm³/g. The porosity (Hg method) due to poreswith radius up to 10,000 Å generally ranges from 0.3 to 1.5 cm³/g,preferably from 0.45 to 1 cm³/g.

As explained above, when a stereospecific catalyst is desired, anelectron donor compound is used in the preparation of the solid catalystcomponent. The so-called internal electron-donor compound may beselected from esters, ethers, amines and ketones. It is preferablyselected from alkyl, cycloalkyl or aryl esters of monocarboxylic acids,for example benzoic acid, or polycarboxylic acids, for example phthalicor malonic acid, the said alkyl, cycloalkyl or aryl groups having from 1to 18 carbon atoms. Examples of preferred electron-donor compounds aremethyl benzoate, ethyl benzoate, diisobutyl phthalate, di-n-hexylphthalate, di-octyl phthalate, di-neopentyl phthalate. Furthermore, theelectron donor compound can be suitably selected from 1,3-diethers offormula (I)

where R^(I) and R^(II) are the same or different and are hydrogen orlinear or branched C₁-C₁₈

hydrocarbon groups which can also form one or more cyclic structures;R^(III) groups, equal or different from each other, are hydrogen orC₁-C₁₈ hydrocarbon groups; R^(IV) groups equal or different from eachother, have the same meaning of R^(IIII) except that they cannot behydrogen; each of R^(I) to R^(IV) groups can contain heteroatomsselected from halogens, N, O, S and Si.

Preferably, R^(IV) is a 1-6 carbon atom alkyl radical and moreparticularly a methyl while the R^(III) radicals are preferablyhydrogen. Moreover, when R^(I) is methyl, ethyl, propyl, or isopropyl,R^(II) can be ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl,isopentyl, 2-ethylhexyl, cyclopentyl, cyclohexyl, methylcyclohexyl,phenyl or benzyl; when R^(I) is hydrogen, R^(II) can be ethyl, butyl,sec-butyl, tert-butyl, 2-ethylhexyl, cyclohexylethyl, diphenylmethyl,p-chlorophenyl, 1-naphthyl, 1 -decahydronaphthyl; R^(I) and R^(II) canalso be the same and can be ethyl, propyl, isopropyl, butyl, isobutyl,tert-butyl, neopentyl, phenyl, benzyl, cyclohexyl, cyclopentyl.

Specific examples of ethers that can be advantageously used include:2-(2-ethylhexyl) 1,3-dimethoxypropane, 2-isopropyl-1,3-dimethoxypropane,2-butyl- ,3-dimethoxypropane, 2-sec-butyl- 1,3-dimethoxypropane,2-cyclohexyl- 1,3-dimethoxypropane, 2-phenyl- 1,3-dimethoxypropane,2-tert-butyl- 1,3-dimethoxypropane, 2-cumyl- 1,3-dimethoxypropane,2-(2-phenylethyl)-1,3-dimethoxypropane,2-(2-cyclohexylethyl)-1,3-dimethoxypropane,2-(p-chlorophenyl)-1,3-dimethoxypropane,2-(diphenylmethyl)-1,3-dimethoxypropane,2(1-naphthyl)-1,3-dimethoxypropane,2(p-fluorophenyl)-1,3-dimethoxypropane,2(1-decahydronaphthyl)-1,3-dimethoxypropane,2(p-tert-butylphenyl)-1,3-dimethoxypropane,2,2-dicyclohexyl-1,3-dimethoxypropane, 2,2-diethyl-1,3-dimethoxypropane,2,2-dipropyl-1,3-dimethoxypropane, 2,2dibutyl-1,3-dimethoxypropane,2,2-diethyl-1,3-diethoxypropane, 2,2-dicyclopentyl-1,3-dimethoxypropane,2,2-dipropyl- 1,3-diethoxypropane, 2,2-dibutyl-1,3-diethoxypropane,2-methyl-2-ethyl-1,3-dimethoxypropane,2-methyl-2-propyl-1,3-dimethoxypropane,2-methyl-2-benzyl-1,3-dimethoxypropane, 2-methyl-2-phenyl-1,3-dimethoxypropane, 2-methyl-2-cyclohexyl-1,3-dimethoxypropane,2-methyl-2-methylcyclohexyl-1,3-dimethoxypropane,2,2-bis(p-chlorophenyl)-1,3-dimethoxypropane, 2,2-bis(2-phenylethyl)-1,3-dimethoxypropane, 2,2-bis(2-cyclohexylethyl)-1,3-dimethoxypropane,2-methyl-2-isobutyl-1,3-dimethoxypropane,2-methyl-2-(2-ethylhexyl)-1,3-dimethoxypropane,2,2-bis(2-ethylhexyl)-1,3-dimethoxypropane,2,2-bis(p-methylphenyl)-1,3-dimethoxypropane,2-methyl-2-isopropyl-1,3-dimethoxypropane,2,2-diisobutyl-1,3-dimethoxypropane,2,2-diphenyl-1,3-dimethoxypropane,2,2-dibenzyl-1,3-dimethoxypropane,2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane,2,2-bis(cyclohexylmethyl)-1,3-dimethoxypropane,2,2-diisobutyl-1,3-diethoxypropane, 2,2-diisobutyl-1,3-dibutoxypropane,2-isobutyl-2-isopropyl- 1,3-dimetoxypropane,2,2-di-sec-butyl-1,3-dimetoxypropane, 2,2-di-tert-butyl-1,3-dimethoxypropane, 2,2-dineopentyl-1,3-dimethoxypropane,2-iso-propyl-2-isopentyl-1,3-dimethoxypropane,2-phenyl-2-benzyl-1,3-dimetoxypropane,2-cyclohexyl-2-cyclohexylmethyl-1,3-dimethoxypropane. Particularlypreferred are the 1,3-diethers of formula (II)

where the radicals R^(III) and R^(IV) have the same meaning explainedabove and the radicals R^(V), equal or different to each other, areselected from the group consisting of hydrogen; halogens, preferably Cland F; C₁-C₂₀ alkyl radicals, linear or branched; C₃-C₂₀ cycloalkyl,C₆-C₂₀ aryl, C₇-C₂₀ alkaryl and C₇-C₂₀ aralkyl radicals and two or moreof the R^(V) radicals can be bonded to each other to form condensedcyclic structures, saturated or unsaturated, optionally substituted withR^(VI) radicals selected from the group consisting of halogens,preferably Cl and F; C₁-C₂₀ alkyl radicals, linear or branched; C₃-C₂₀cycloalkyl C₆-C₂₀ aryl, C₇-C₂₀ alkaryl and C₇-C₂₀ aralkyl radicals; saidradicals R^(V) and R^(VI) optionally containing one or more heteroatomsas substitutes for carbon or hydrogen atoms, or both. Preferably, in the1,3-diethers of formulae (I) and (II) all the R^(III) radicals arehydrogen, and all the R^(IV) radicals are methyl. Moreover, areparticularly preferred the 1,3-diethers of formula (II) in which two ormore of the R^(V) radicals are bonded to each other to form one or morecondensed cyclic structures, preferably benzenic, optionally substitutedby R^(VI) radicals. Specially preferred are the compounds of formula(III):

where the R^(VI) radicals equal or different are hydrogen; halogens,preferably Cl and F; C₁-C₂₀ alkyl radicals, linear or branched; C₃-C₂₀cycloalkyl, C₆-C₂₀ aryl, C₇-C₂₀ alkylaryl and C₇-C₂₀ aralkyl radicals,optionally containing one or more heteroatoms selected from the groupconsisting of N, O, S, P, Si and halogens, in particular Cl and F, assubstitutes for carbon or hydrogen atoms, or both; the radicals R^(III)and R^(IV) are as defined above for formula (II). Specific examples ofcompounds comprised in formulae (II) and (III) are:

1,1-bis(methoxymethyl)-cyclopentadiene;

1,1-bis(methoxymethyl)-2,3,4,5-tetramethylcyclopentadiene;

1,1-bis(methoxymethyl)-2,3,4,5-tetraphenylcyclopentadiene;

1,1-bis(methoxymethyl)-2,3,4,5-tetrafluorocyclopentadiene;

1,1-bis(methoxymethyl)-3,4-dicyclopentylcyclopentadiene;

1,1-bis(methoxymethyl)indene;

1,1-bis(methoxymethyl)-2,3-dimethylindene;

1,1-bis(methoxymethyl)-4,5,6,7-tetrahydroindene;

1,1-bis(methoxymethyl)-2,3,6,7-tetrafluoroindene;

1,1-bis(methoxymethyl)-4,7-dimethylindene;

1,1-bis(methoxymethyl)-3,6-dimethylindene;

1,1-bis(methoxymethyl)-4-phenylindene;

1,1-bis(methoxymethyl)4-phenyl-2-methylindene;

1,1-bis(methoxymethyl)4-cyclohexylindene;

1,1-bis(methoxymethyl)-7-(3,3,3-trifluoropropyl)indene;

1,1-bis(methoxymethyl)-7-trimethyisilylindene;

1,1-bis(methoxymethyl)-7-trifluoromethylindene;

1,1-bis(methoxymethyl)-4,7-dimethyl-4,5,6,7-tetrahydroindene;

1,1-bis(methoxymethyl)-7- methylindene;

1,1-bis(methoxymethyl)-7-cyclopenthylindene;

1,1-bis(methoxymethyl)-7-isopropylindene;

1,1-bis(methoxymethyl)-7-cyclohexylindene;

1,1-bis(methoxymethyl)-7-tert-butylindene;

1,1-bis(methoxymethyl)-7-tert-butyl-2-methylindene;

1,1-bis(methoxymethyl)-7-phenylindene;

1,1-bis(methoxymethyl)-2-phenylindene;

1,1-bis(methoxymethyl)-1H-benz[e]indene;

1,1-bis(methoxymethyl)-1H-2-methylbenz[e]indene;

9,9-bis(methoxymethyl)fluorene;

9,9-bis(methoxymethyl)-2,3,6,7-tetramethylfluorene;

9,9-bis(methoxymethyl)-2,3,4,5,6,7-hexafluorofluorene;

9,9-bis(methoxymethyl)-2,3-benzofluorene;

9,9-bis(methoxymethyl)-2,3,6,7-dibenzofluorene;

9,9-bis(methoxymethyl)-2,7-diisopropylfluorene;

9,9-bis(methoxymethyl)-1,8-dichlorofluorene;

9,9-bis(methoxymethyl)-2,7-dicyclopentylfluorene;

9,9-bis(methoxymethyl)-1,8-difluorofluorene;

9,9-bis(methoxymethyl)-1,2,3,4-tetrahydrofluorene;

9,9-bis(methoxymethyl)-1,2,3,4,5,6,7,8-octahydrofluorene;

9,9-bis(methoxymethyl)4-tert-butylfluorene.

9,9-bis(methoxymethyl)fluorene being the most preferred.

Most preferred internal electron donors for use in the preparation ofthe catalyst components of the present invention are the esters ofphthalic acid and the above described 1,3 diethers. In the preparationmethods described above, the internal electron donor compound can beadded as such or, in an alternative way, it can be obtained in situ byusing an appropriate precursor capable to be transformed in the desiredelectron donor compound by means, for example, of known chemicalreactions such as esterification or transesterification. Generally, theinternal electron donor compound is added in molar ratio with respect tothe MgCl₂ of from 0.01 to 1 preferably from 0.05 to 0.5.

The solid catalyst components used to prepare the pre-polymer can alsobe prepared according to the disclosure of WO 95/32995 in which a Ti, Zror Hf metallocene compound is supported on a MgCl₂ having surface areahigher than 100 m²/g and porosity (BET) higher than 0.2 cm³/g.

As explained above, the original solid catalyst component is thenpre-polymerized with one or more olefins or diolefins to obtain theporous pre-polymer. Generally, the pre-polymer has the same nature asthe final polymer to be produced but, if deemed it advisable, thepre-polymer can also have a different nature with respect to the finalpolymer. This can be the case for example when the pre-polymer has towork as a nucleating agent which is homogeneously dispersed within thefinal product.

Suitable olefins to be prepolymerized are those of formula CH₂═CHR,wherein R is hydrogen or a C1-C12 alkyl group or an aryl radical.Preferably, the olefin is selected from ethylene, propylene, butene-1,hexene-1, and 4-methyl-1-pentene. Ethylene and propylene are especiallypreferred.

Preferably, the pre-polymer is prepared under conditions such as toobtain a crystalline polymer, and in particular, polymers having a highcontent of crystallinity. In the case of the pre-polymerization ofpropylene for example, the preferred polypropylenes are those having acrystallinity such that the fusion enthalpy, measured by DSC method ishigher than 70 J/g . The pre-polymerization is generally carried out inthe presence of an alkyl-aluminum compound. The alkyl-Al compound (B) ispreferably chosen among the trialkyl aluminum compounds such as forexample triethylaluminum (TEAL), triisobutylaluminum,tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It isalso possible to use mixtures of trialkylaluminum's with alkylaluminumhalides alkylaluminum hydrides or alkylaluminum sesquichlorides such asAlEt₂Cl and Al₂Et₃Cl₃. It is further possible to use an metallo-alkylcompound different from an alkyl-Al compound, such as zinc di-alkylcompound capable of promoting olefin polymerization when used togetherwith a Ti compound containing Ti-halogen bonds.

When the catalyst components comprise a metallocene compound supportedon Mg dihalide, the Al-alkyl is suitably selected from alumoxanescontaining the repeating unit —(R^(I))—Al—O— in which R^(I) , equal ordifferent to each other are hydrocarbon groups having from 1 to 20carbon atoms

The amount of Al-alkyl compound generally used is such as to have anAl/Ti molar ratio of from 1 to 50. In the present invention it has beenfound particularly advantageous to carry out said pre-polymerizationusing lower amounts of alkyl-Al compound. In particular, said amount canbe as low as to have an Al/Ti molar ratio of from 0.01 to 10 and morepreferably of from 0.05 to 5.

During the pre-polymerization step, the presence of an external donor isnot strictly necessary. However, it can be used in amounts such as togive Al/donor molar ratios ranging from 0.1 to 300 and preferably from 1to 50. The external electron donor compound can be the same as, ordifferent from, the internal donor described above. SuiTable externalelectron donor compounds include silicon compounds, ethers, esters,amines, heterocyclic compounds and particularly 2,2,6,6-tetramethylpiperidine, ketones and the 1,3-diethers of the general formula (I)given above.

A class of preferred external donor compounds, to be used in particularwhen the internal donor is a phthalate, is that of silicon compounds offormula R⁵ _(a)R⁶ _(b)Si(OR⁷)_(c), where a and b are integers of from 0to 2, c is an integer of from 1 to 3 and the sum (a+b+c) is 4; R⁵, R⁶,and R⁷, are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atomsoptionally containing heteroatoms. Particularly preferred are thesilicon compounds in which a is 1, b is 1, c is 2, at least one of R⁵and R⁶ is selected from branched alkyl, cycloalkyl or aryl groups with3-10 carbon atoms optionally containing heteroatoms and R⁷ is a C₁-C₁₀alkyl group, in particular methyl. Examples of such preferred siliconcompounds are methylcyclohexyldimethoxysilane, diphenyldimethoxysilane,methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane,2-ethylpiperidinyl-2-t-butyldimethoxysilane and1,1,1,trifluoropropyl-2-ethylpiperidinyl-dimethoxysilane. Moreover, arealso preferred the silicon compounds in which a is 0, c is 3, R⁶ is abranched alkyl or cycloalkyl group, optionally containing heteroatoms,and R⁷ is methyl. Examples of such preferred silicon compounds arecyclohexyltrimethoxysilane, t-butyltrimethoxysilane andthexyltrimethoxysilane.

In particular when esters of monocarboxylic acids, for examplebenzoates, are used as internal donors also the external donor compoundis selected from this class, p-ethoxy-ethyl benzoate being the mostpreferred. In addition, a mixture of this donor with another one, and inparticular one selected from the class of silicon compounds, can beused. In this case ethylcyclohexyldimethoxysilane anddicyclopentyldimethoxysilane are most preferred. The pre-polymerizationcan be carried out in liquid phase, (slurry or solution) or in gas-phaseat temperatures generally lower than 80° C., preferably in the rangebetween −20 and 60° C. Furthermore, it is preferably carried out in aliquid diluent in particular selected from liquid hydrocarbons. Amongthem, pentane, hexane and heptane are preferred.

The catalyst component of the present invention is then obtained bycontacting the pre-polymer prepared according to the above procedurewith the Ti compound as previously defined.

The Ti compound is preferably liquid under normal conditions, i.e. roomtemperature and atmospheric pressure. When the Ti compound is a solid,it is used in solution in a suitable solvent which is inert towards thepre-polymer and towards the catalyst components contained therein andwhich can be removed from the Ti compound by heating and/or chemicalreaction with compounds such as SiCl₄ or Al-alkyl compounds.

Preferably, the Ti compound is selected from the group consisting ofhalides and, among them, the use of TiCl₄ is especially preferred.

The contact of the pre-polymer with the Ti compound is carried out underconditions suitable to fix at least 0.05% of Ti compound, expressed asTi, on the pre-polymerized catalyst component. A Ti compound isconsidered fixed on the pre-polymerized catalyst component when it isnot extractable to an extent higher than 50% with heptane at 80° C. for2 hours. The amount of Ti compound fixed on the pre-polymerized catalystcomponent by effect of the contact stage is generally higher than 0.05%,preferably higher than 0.2%, expressed as Ti.

In particular, when a Ti-based catalyst component is used to prepare thepre-polymer, the total amount of Ti compound (expressed as Ti) after thecontact stage is from 0.1 to 5% preferably from 0.15 to 3% and morepreferably from 0.2 to 2,5%.

In this case, particularly advantageous are the catalyst componentscontaining Mg dichloride in amount of 50 to 50,000 ppm, expressed as Mg,and in which the total amount of Ti compound fixed on thepre-polymerized catalyst component is such as to have a Ti/Mg weightratio of from 0.01 to 3.and preferably from 0.1 to 2.5.

According to one of the preferred methods the pre-polymer is reactedwith an excess of neat TiCl₄ at a temperature between 40 and 120°,preferably from 60 and 90° C. for a period of time ranging from 0.2 to 2h. At the end of the treatment the excess of TiCl₄ is removed bysiphoning or filtration of the solid component. Preferably, the reactionwith TiCl₄ is carried out two or more times. Moreover, it is especiallypreferred carrying out said reaction in the presence of an electrondonor compound dissolved in the TiCl₄. Preferably, the electron donorcompound is selected from the groups disclosed above as suitableinternal electron donor compounds.

According to another method the reaction is carried out with TiCl₄diluted in a suitable hydrocarbon compound such as pentane, hexane,heptane, toluene. Also in this case the use of an internal electrondonor compound is preferred.

After the contact stage with the Ti compound is completed thepre-polymerized catalyst component is suitably washed with solvents, inorder to remove compounds not fixed on it. The washings are generallycarried out at temperatures comprised between the room temperature andthe boiling point of the solvent used. Suitable solvents to be usedinclude liquid hydrocarbons such as hexane, heptane, toluene andhalogenated hydrocarbons such as CH₂Cl₂.

The thus obtained pre-polymerized catalyst components allow to obtainhighly active catalysts. In particular, when used in the polymerizationof propylene, allow to obtain polymers with high stereoregularity, highbulk density and very good morphology thus showing their particularsuitability for the liquid (bulk or slurry) and gas-phase processes. Inparticular, the pre-polymerized catalyst components of the inventionshow activities referred to the Mg that are remarkably improved withrespect to those of the original solid component used to prepare thepre-polymer. Also, the yields referred to the pre-polymer/catalystsystem are higher than the yields of the pre-polymer catalyst/system nottreated with the Ti compound.

In view of these peculiarities, the catalyst components of the inventionare particularly suitable for the use in liquid or gas-phase olefinpolymerization plants operating without a pre-polymerization line.

In particular, said olefin polymerization processes are be carried outin the presence of a catalyst comprising (A) the pre-polymerizedcatalyst component described above; (B) a suitable cocatalyst,particularly an Al-alkyl compound, and optionally (C) one or moreelectron donor (external) compounds.

These latter can be selected from the groups of compounds that have beendisclosed above as suitable external electron compounds and according tothe guidance already described. In the main polymerization step theelectron donor compound (C) is used in such an amount to give a molarratio between the organoaluminum compound and said electron donorcompound of from 0.1 to 500, preferably from 1 to 300 and morepreferably from 2 to 100. The Al/Ti ratio is preferably higher than 10.

The Al-alkyl compounds are preferably selected from those of formulaR_(z)AlX_(3-z), in which R is a C₁-C₂₀ hydrocarbon group, particularlyan alkyl, isoalkyl, cycloalkyl or aryl radical, z is 2 or 3 and X is anhalogen atom, preferably chlorine. Particularly preferred is the use ofthe trialkyl aluminum compounds such as for example triethylaluminum(TEAL), triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum,tri-n-octylaluminum and tris(2,4,4-trimethyl-pentyl)aluminum. It is alsopossible to use mixtures of trialkylaluminum compounds withalkylaluminum halides, alkylaluminum hydrides or alkylaluminumsesquichlorides, such as AlEt₂Cl and Al₂Et₃Cl₃.

Another class of compounds suitable as catalyst components to preparethe pre-polymer is that of the metallocene compounds having at least oneM—R link in which M is Ti, Zr, or Hf and R is an alkyl radical. Saidmetallocene compounds are used in amounts such as to be in an equimolarratio or in excess with respect to the metal compound present in thecatalyst component. Preferably, said ratio ranges from 2:1 to 30:1. Incase an equimolar amount of cocatalyst is used it is preferred adding ascavenger compound to the system selected from Al, Mg or Zn alkylcompounds that are not able to promote olefin polymerization whenemployed together with compounds containing Ti-halogen bonds. Examplesof these compounds are Zn diethyl, Mg diethyl and AlEt₃ complexed withethers or electron donor compounds not containing active hydrogen atoms.

Suitable metallocene compounds having at least one M—R link aregenerally those comprising two cyclopentadienyl rings, coordinated withthe metal, which can be substituted and/or bridged and possiblycondensed with other rings. Representative compounds are specificallymentioned and described in WO95/26369 the relevant part of which isherein included by reference.

In case the catalyst components comprise a metallocene compound, it isadvisable to use, alone or in combination with another Al-alkylcompound, an alumoxane selected from those containing the repeating unit—(R¹)—Al—O— in which R¹, equal or different to each other arehydrocarbon groups having from 1 to 20 carbon atoms. The use ofmethylalumoxane is preferred. In addition, it is also possible to usecompounds of the formula Y⁺Z⁻, where Y+ is a Brönsted acid capable ofdonating a proton and irreversibly reacting with a substituent of themetallocene compound, and Z⁻ is a compatible not coordinating anionwhich is capable of stabilizing the active catalytic species resultingfrom the reaction of the two compounds and which is sufficiently labileto be displaced by an olefinic substrate. Preferably, the anion Z⁻consists of one or more boron atoms. More preferably, the anion Z⁻ is ananion of the formula BAr₄ ⁻, where the substituents Ar which can beidentical or different are aryl radicals such as phenyl,pentafluorophenyl or bis(trifluoro-methyl)phenyl.Tetrakis-pentafluorophenyl borate is particularly preferred. Moreover,compounds of the formula BAr₃ can conveniently be used. Compounds ofthis type are described for example, in the International patentapplication WO92/00333.

The above described polymerization process can be carried out under thepolymerization conditions generally known in the art. Accordingly, thepolymerization is generally carried out at a temperature of from 20 to120° C., preferably of from 40 to 80° C. When the polymerization iscarried out in gas-phase the operating pressure is generally between 0.5and 10 MPa, preferably between 1 and 5 MPa. In the bulk polymerizationthe operating pressure is generally between 1 and 6 MPa preferablybetween 1.5 and 4 MPa.

In any of the polymerization processes used (liquid or gas-phasepolymerization) the catalyst forming components (A), (B) and optionally(C), can be pre-contacted before adding them to the polymerizationreactor. Said pre-contacting step can be carried out in the absence ofpolymerizable olefin or optionally in the presence of said olefin in anamount up to 3 g per g of solid catalyst component. The catalyst formingcomponents can be contacted with a liquid inert hydrocarbon solvent suchas propane, n-hexane, or n-heptane at a temperature below about 60° C.and preferably from about 0° C. to 30° C. for a time period of from 10seconds to 60 minutes.

When a gas-phase polymerization process is used, it can be carried outaccording to known techniques operating in ore or more reactors having afluidized or mechanically agitated bed. Inert fluids such as nitrogen,or low hydrocarbons like propane, can be used both as a fluidization aidand in order to improve the thermal exchange within the reactors. Inaddition, also techniques increasing the removal of the reaction heatcomprising the introduction of liquids, optionally in mixture with gas,into the reactors, can be used. Preferably the liquids are fresh ormake-up monomers. Such techniques are disclosed for example inEP-A-89691, EP-A-241947, U.S. Pat. No. 5,352,749, WO94/28032 andEPA-695313.

Among the olefin polymers obtainable by the process of the invention,particularly interesting are the propylene (co)polymers having a heat offusion (ΔHf) higher than 70 J/g measured by D.S.C. method.

The following examples are given in order better illustrate theinvention without limiting it.

EXAMPLES

Characterization

Crystallite Dimension

Determined by measuring the breadth at half-height of the (110)reflection appearing in the spectrum of the magnesium halide applyingthe Sherrer's equation D(110)=(K·1.542·57.3)/(B−b)cos θ where:

K=constant (1.83 in the case of Mg chloride)

B=breadth at half-height;

B=instrumental broadening;

cos θ=Bragg angle.

The X-ray diffraction spectrum of the catalyst component is carried outwith a diffractometer using the CuK_(a)(λ1,5418 Å) radiation, set with a0.2 mm receiving slit and recording conditions such as to give a numberof counts associated with the (110) reflection of 1000 or higher; saidspectrum being carried out and without adding any standard to thesample.

Determination X.I.

2.5 g of polymer were dissolved in 250 ml of o-xylene under stirring at135EC for 30 minutes, then the solution was cooled to 25° C. and after30 minutes the insoluble polymer was filtered. The resulting solutionwas evaporated in nitrogen flow and the residue was dried and weighed todetermine the percentage of soluble polymer and then, by difference, theX.I. %.

General Procedure for the Standard Propylene Polymerization Test

A 4-liter steel autoclave equipped with a stirrer, pressure gauge,thermometer, catalyst-feeding system, monomer feeding lines andthermostatting jacket, was used. The reactor was charged with 0.01 g ofsolid catalyst component and with TEAL, and cyclohexyl-methyl dimethoxysilane in such amounts to give an Al/Donor molar ratio of 20. Moreover,3.2 l of propylene, and 1 L of hydrogen were added. The system washeated to 70° C. over 10 min. under stirring, and maintained under theseconditions for 120 min. At the end of the polymerization, the polymerwas recovered by removing any unreacted monomers and was dried undervacuum.

General Procedure for the Standard Ethylene Polymerization (HDPE)

Into a 4 liters stainless steel autoclave, degassed under N₂ stream at70° C., 1600 cc of anhydrous hexane, 0.02 g of spherical component and0.3 g of triisobutylaluminum (Tiba) were introduced. The whole wasstirred, heated to 75° C. and thereafter 4 bar of H₂ and 7 bar ofethylene were fed. The polymerization lasted 2 hours during whichethylene was fed to keep the pressure constant. At the end of thepolymerization, the polymer was recovered by removing any unreactedmonomers and was dried under vacuum.

Porosity (Due to Pores with Radius Up to 75,000 Å)

The measure is carried out using a “Porosimeter 2000 series” by CarloErba.

The porosity is determined by absorption of mercury under pressure. Forthis determination use is made of a calibrated dilatometer (diameter 3mm) CD₃ (Carlo Erba) connected to a reservoir of mercury and to ahigh-vacuum pump (1-10² mbar). A weighed amount of sample is placed inthe dilatometer. The apparatus is then placed under high vacuum (<0.1 mmHg) and is maintained in these conditions for 10 minutes. Thedilatometer is then connected to the mercury reservoir and the mercuryis allowed to flow slowly into it until it reaches the level marked onthe dilatometer at a height of 10 cm. The valve that connects thedilatometer to the vacuum pump is closed and then the mercury pressureis gradually increased with nitrogen up to 140 kg/cm². Under the effectof the pressure, the mercury enters the pores and the level goes downaccording to the porosity of the material. The porosity (cm³/g), and thedistribution of pores is directly calculated from the integral poredistribution curve which is function of the volume reduction of themercury and applied pressure values (all these data are provided andelaborated by the porosimeter associated computer which is equipped witha “MILESTONE 200/2.04” program by C. Erba.

Determination of Melt Index

ASTM D 1238 condition “L”

EXAMPLES Example 1

Preparation of Solid Catalyst Component (Example 1A)

10.0 g of microspheroidal MgCl₂.2.8C₂H₅OH (prepared according to themethod described in ex.2 of U.S. Pat. No. 4,399,054 but operating at3,000 rpm instead of 10,000) were subject to thermal dealcoholationcarried out at increasing temperatures from 30 to 95° C. and operatingin nitrogen current until a molar ratio EtOH/MgCl₂ of about 1 wasobtained. The so obtained adduct was poured into a 500 ml four-neckedround flask, purged with nitrogen, which contained 250 ml of TiCl₄introduced at 0° C. The flask was heated to 40° C. and 6 mmoles ofdiisobutylphthalate (DIBP) were thereupon added. The temperature wasraised to 100° C. and maintained for two hours, then the stirring wasdiscontinued, the solid product was allowed to settle and thesupernatant liquid was siphoned off.

The treatment with TiCl₄ was repeated and the solid obtained was washedsix times with anhydrous hexane (6×100 ml) at 60° C. and then driedunder vacuum. A catalyst component having a surface area (measured byBET) of 130m²/g and a porosity (Hg due to pores with radius up to 10,000Å) of 0.72 was obtained. The chemical characteristics of the solid, theresults of the propylene polymerization test and that of the ethylenepolymerization test are reported in Table 1.

Propylene Pre-polymerization (Example 1B).

The catalyst component prepared according to the above procedure waspre-polymerized with propylene to give a weight ratio pre-polymer/solidcatalyst component of 10 g/g. The pre-polymerization was carried out inhexane in the presence of TEAL (weight ratio TEAL/solid catalystcomponent=0.05) and cyclohexyl-methyl-dimethoxy silane as external donor(molar ratio TEAL/Donor of 20). The so obtained pre-polymer catalystsystem, having a porosity (Hg due to pores with radius up to 75,000 Å)of 0.56 cm³/g was subject to the propylene polymerization procedure theresults of which are reported in Table 1.

Treatment Stage with the Ti Compound

The above prepared pre-polymer was suspended in TiCl₄ using amounts ofreactants such as to give a 50 g/l suspension. The temperature was thenraised at 80° C. and the system was kept under these conditions, withstirring, for 1 hour. After that time stirring was discontinued theliquid siphoned off and the solid obtained was washed with hexane. Thechemical characteristics of the solid, the results of the propylenepolymerization test and that of the ethylene polymerization test arereported in Table 1.

Example 2

The pre-polymer prepared according to the procedure of example 1, wassuspended in liquid TiCl₄ also containing DIBP. The amounts of reactantswere such as to give a concentration of pre-polymer in TiCl₄ of 50 g/land weight ratio DIBP/pre-polymer of 12%. The temperature was thenraised at 80° C. and the system was kept under these conditions, withstirring, for 1 hour. After that time stirring was discontinued theliquid siphoned off. A further stage of contacting with TiCl₄, withoutDIBP, under the same conditions was performed at the end of which thesolid was washed with hexane at 60° C. The chemical characteristics ofthe solid, the results of the propylene polymerization test and that ofthe ethylene polymerization test are reported in Table 1.

Example 3

The pre-polymer prepared according to the procedure of example 1, wassuspended in liquid medium containing heptane and TiCl₄ in a 1:1 volumeratio and also containing 9,9-bis(methoxymethyl)fluorene. The amounts ofreactants were such as to give a concentration of pre-polymer in theliquid phase of 50 g/l and a weight ratio9,9-bis(methoxymethyl)fluorene/pre-polymer of 5%. The temperature wasthen raised at 80° C. and the system was kept under these conditions,with stirring, for 1 hour. After that time stirring was discontinued theliquid siphoned off. A further stage of contacting with pure TiCl₄without 9,9-bis(methoxymethyl)fluorene, under the same conditions asthose disclosed in example 1 was performed at the end of the solid waswashed with hexane. The chemical characteristics of the solid, theresults of the propylene polymerization test and that of the ethylenepolymerization test are reported in Table 1.

Example 4

The same pre-polymerization procedure disclosed in Example 1 wasrepeated with the only difference that the pre-polymerization wasprolonged up to obtaining a final weight ratio pre-polymer/catalyst of15g/g.

Treatment Stage with the Ti Compound

The treatment was carried out according to the procedure disclosed inexample 1. The chemical characteristics of the solid, the results of thepropylene polymerization test and that of the ethylene polymerizationtest are reported in Table 1.

Example 5

Ethylene Pre-Polymerization

The catalyst component prepared according to the procedure disclosed inExample 1 was pre-polymerized with ethylene to give a weight ratiopre-polymer/catalyst of 11.6 g/g. The pre-polymerization was carried outin hexane using TEAL as cocatalyst (weight ratio TEAL/solid catalystcomponent=0.05). The so obtained pre-polymer catalyst system, having aporosity (Hg due to pores with radius up to 75,000 Å) of 0.6 cm³/g wassubject to the propylene polymerization procedure and to the ethylenepolymerization procedure the results of which are reported in Table 1.

Treatment Stage with the Ti Compound

The obtained ethylene pre-polymer, was suspended in liquid mediumcontaining heptane and TiCl₄ in a 1:1 volume. The amounts of reactantswere such as to give a concentration of pre-polymer in the liquid phaseof 50 g/l. The temperature was then raised at 80° C. and the system waskept under these conditions, with stirring, for 1 hour. After that timestirring was discontinued the liquid siphoned off and the solid washedwith hexane at 60° C. The chemical characteristics of the solid, theresults of the propylene polymerization test are reported in Table 1.

Example 6

Treatment Stage with the Ti Compound

The ethylene pre-polymer according to example 5 was suspended in liquidmedium containing heptane/TiCl₄ in a 1:1 volume ratio and alsocontaining 9,9-bis(methoxymethyl)fluorene. The amounts of reactants weresuch as to give a concentration of pre-polymer in the liquid phase of 50g/l and a weight ratio 9,9-bis(methoxymethyl)fluorene/pre-polymer of 5%.The temperature was then raised at 80° C. and the system was kept underthese conditions, with stirring, for 1 hour. After that time stirringwas discontinued the liquid siphoned off and a further treatment withTiCl₄, without 9,9-bis(methoxymethyl)fluorene was carried out. At theend the solid was washed with hexane and then dried. The chemicalcharacteristics of the solid, the results of the propylenepolymerization test and that of the ethylene polymerization test arereported in Table 1.

Example 7

Ethylene Pre-Polymerization

The catalyst component prepared according to the procedure disclosed inExample 1 was pre-polymerized with ethylene to give a weight ratiopre-polymer/catalyst of 30 g/g. The pre-polymerization was carried outin hexane using TEAL as cocatalyst (weight ratio TEAL/solid catalystcomponent=0.5). The so obtained pre-polymer catalyst system, having aporosity (Hg due to pores with radius up to 75,000 Å) of 0.6 cm³/g wassubject to the propylene polymerization procedure the results of whichare reported in Table 1.

Treatment Stage with the Ti Compound

The ethylene pre-polymer according to Example 5 was suspended in liquidmedium containing heptane/TiCl₄ in a 1:1 volume ratio and alsocontaining DIBP. The amounts of reactants were such as to give aconcentration of pre-polymer in the liquid phase of 50 g/l and a weightratio DIBP/pre-polymer of 5%. The temperature was then raised at 80° C.and the system was kept under these conditions, with stirring, for 1hour. After that time stirring was discontinued the liquid siphoned offand a further treatment with TiCl₄, without DIBP was carried out. At theend the solid was washed with hexane and then dried. The chemicalcharacteristics of the solid, the results of the propylenepolymerization test are reported in Table 1.

TABLE 1 ANALYSIS PROPYLENE ETHYLENE Ti Mg DIBP Et. POLYMERIZATIONPOLYMERIZATION EXAMPLE (w %) (w %) (w %) (w %) Activity^((a))Activity^((b)) X. I. Activity^((a)) Activity^((b)) 1A 2.1 20.1 5.8 — —15.3 96.6 — 15 1B 0.2 1.92 0.6 — 1.04 11 95.8 — — 1 0.56 2.1 0.3 — 2.526.5 92 2 21 2 2.2 1.7 9 — 2.3 24 95 1.9 20 3 0.57 1.9 1.3 3.4(*) 35(*)92(*) 3.2 33.6 2.9(+) 30.5(+) 96.6(+) 4 0.94 1.72 0.2 — 1.7 26 n.d. 3.958 5 0.5 1.5 0.1 — 2 23.2 n.d. 1.9 22 6 0.4 1.6 1   2.6(*) 30.2(*)93.5(*) — — 2(+) 24.3(+) 96.2(+) 7 0.65 0.6 0.6 — 1 30 96 — —Activity^((a)): Activity expressed in terms of Kg of polymer per g ofpre-polymer fed Activity^((b)): Activity expressed in terms of Kg ofpolymer per g of cat. comp. contained in the pre-polymer (*):Polymerization carried out in the absence of external donor (+):Polymerization carried out with dicyclopentyldimethoxysilane as externaldonor with a TEAL/donor ratio of 60 Et.: 9,9-bis(methoxymethyl)fluorenen.d. = not determined

What is claimed is:
 1. Catalyst component for the polymerization ofolefins CH₂═CHR, wherein R is hydrogen or a hydrocarbon radical having1-12 carbon atoms, comprising the product obtained by contacting a Ticompound of formula Ti(OR)_(n−y)X_(y), where R is an alkyl, isoalkyl,cycloalkyl or aryl radical having from 1 to 18 carbon atoms, X is ahalogen atom, n is the valence of titanium and y is a number of from 1to n, with a pre-polymer having a porosity (measured with Hg method)higher than 0.3 cc/g and containing from 0.5 to 100 g of polymer per gof a solid catalyst component, said pre-polymer being obtained by(co)polymerizing an olefin or a diolefin which is (co)polymerizable inthe presence of a catalyst comprising the solid catalyst component, thesolid catalyst component comprising a transition metal compound selectedfrom the group consisting of Ti compounds of the above formulaTi(OR)_(n−y)X_(y), vanadium halides, haloalcoholates and vanadylhalides, and Ti, Zr and Hf compounds containing at least a π-metal bond,said transition metal compound being supported on a Mg dihalide having amean crystallite size lower than 30 nm.
 2. Catalyst components accordingto claim 1 in which the contact of the pre-polymer with the Ti compoundis carried out under conditions suitable to fix at least 0.05 wt % of Ticompound, expressed as Ti.
 3. Catalyst component according to claim 2 inwhich the Ti compound fixed on the pre-polymer is higher than 0.2 wt %,expressed as Ti.
 4. Catalyst components according to claim 1 in whichthe Mg dihalide has a mean crystallite size lower than 15 nm. 5.Catalyst component according to claim 1 in which the porosity of thepre-polymer is higher than 0.4 cm³/g.
 6. Catalyst component according toclaim 5 in which the porosity of the pre-polymer is higher than 0.5cm³/g.
 7. Catalyst component according to claim 1 in which the amount ofpre-polymer ranges from 1 to 50 g of polymer per g of solid catalystcomponent used to prepare it.
 8. Catalyst component according to claim 7in which the amount of pre-polymer ranges from 2 to 30 g of polymer perg of solid catalyst component.
 9. Catalyst components according to claim1 in which the solid catalyst component used to prepare the pre-polymeris obtained by reacting a titanium compound of formulaTi(OR)_(n−y)X_(y), where R is an alkyl, isoalkyl, cycloalkyl or arylradical having from 1 to 18 carbon atoms, X is a halogen atom, n is thevalence of titanium and y is a number of from 1 to n, with an adduct offormula MgCl₂.pROH, where p is a number of from 0.1 to 6 and R is analkyl, isoalkyl or cycloalkyl radical having 1-18 carbon atoms. 10.Catalyst components according to claim 9 in which the Ti compound isTiCl₄.
 11. Catalyst components according to claim 1 in which the solidcatalyst component used to prepare the pre-polymer has a surface area(by B.E.T. method) between 20 and 500 m²/g and a porosity (Hg method)due to pores with radius up to 10,000 Å from 0.3 to 1.5 cm³/g. 12.Catalyst components according to claim 1 in which the solid catalystcomponent used to prepare the pre-polymer contain an internalelectron-donor compound selected from esters, ethers, amines or ketones.13. Catalyst components according to claim 12 in which the internaldonor is selected from alkyl, cycloalkyl or aryl esters ofmonocarboxylic or polycarboxylic acids.
 14. Catalyst componentsaccording to claim 13 in which the internal donor is selected frommethyl benzoate, ethyl benzoate, diisobutyl phthalate, di-n-hexylphthalate, di-octyl phthalate, or di-neopentyl phthalate.
 15. Catalystcomponents according to claim 12 in which the internal donor is selectedfrom 1,3-diethers of formula (I)

where R^(I) and R^(II) are the same or different and are hydrogen orlinear or branched C₁-C₁₈ hydrocarbon groups which can also form one ormore cyclic structures; R^(III) groups, equal or different from eachother, are hydrogen or C₁-C₁₈ hydrocarbon groups; R^(IV) groups equal ordifferent from each other, have the same meaning of R^(III) except thatthey cannot be hydrogen; each of R^(I) to R^(IV) groups can containheteroatoms selected from halogens, N, O, S or Si.
 16. Catalystcomponents according to claim 15 in which the internal electron donorcompound is selected from 1,3-diethers of formula (II)

where the radicals R^(IV) have the same meaning explained in claim 15and the radicals R^(III) and R^(V), equal or different to each other,are selected from the group consisting of hydrogen, halogens, C₁-C₂₀alkyl radicals, linear or branched; C₃-C₂₀ cycloalkyl, C₆-C₂₀ aryl,C₇-C₂₀ alkaryl and C₇-C₂₀ aralkyl radicals and two or more of the R^(V)radicals can be bonded to each other to form condensed cyclicstructures, saturated or unsaturated, optionally substituted with R^(VI)radicals selected from the group consisting of halogens, C¹-C₂₀ alkylradicals, linear or branched; C₃-C₂₀ cycloalkyl, C₆-C₂₀ aryl, C₇-C₂₀alkaryl and C₇-C₂₀ aralkyl radicals; said radicals R^(V) and R^(VI)optionally containing one or more heteroatoms as substitutes for carbonor hydrogen atoms, or both.
 17. Catalyst components according to claim16 in which the internal electron donor compound is selected from thecompounds of formula (III):

where the R^(VI) radicals equal or different are hydrogen; halogens,C₁-C₂₀ alkyl radicals, linear or branched; C₃-C₂₀ cycloalkyl, C₆-C₂₀aryl, C₇-C₂₀ alkylaryl and C₇-C₂₀ aralkyl radicals, optionallycontaining one or more heteroatoms selected from the group consisting ofN, O, S, P, Si and halogens as substitutes for carbon or hydrogen atoms,or both; the radicals R^(III) and R^(IV) are as defined in claim 16 forformula (II).
 18. Catalyst components according to claim 17 in which theinternal electron donor compound is 9,9-bis(methoxymethyl)fluorene. 19.Catalyst components according to claim 1 in which the pre-polymer isobtained by pre-polymerizing ethylene or propylene.
 20. Catalystcomponents according to claim 1 in which the pre-polymer is acrystalline pre-polymer.
 21. Catalyst components according to claim 10in which the catalyst used to prepare the pre-polymer further comprisesan Al-alkyl compound used in amount such as to give an Al/Ti ratio offrom 0.01 to
 10. 22. Catalyst components according to claim 21 in whichthe Al/Ti ratio is from 0.05 to
 5. 23. Catalyst components according toclaim 1 in which the Ti compound contacted with the pre-polymer isTiCl₄.
 24. Catalyst components for the polymerization of olefinsCH₂═CHR, wherein R is hydrogen or a hydrocarbon radical having 1-12carbon atoms, comprising a Ti compound of formula Ti(OR)_(n−y)X_(y),where n is the valence of titanium and y is a number of from 1 to n,fixed on a pre-polymerized catalyst component containing Mg dichloridein amount of 50 to 50,000 ppm, expressed as Mg, said Ti compound beingpresent in a Ti/Mg weight ratio from 0.01 to
 3. 25. Catalysts for thepolymerization of olefins comprising (A) a catalyst component accordingto claim 1, (B) a cocatalyst and, optionally, (C) one or more externalelectron donor compounds.
 26. Catalyst according to claim 25 in whichthe cocatalyst (B) is selected from Al-alkyl compounds of formulaR_(z)AlX_(3−z) in which R is a C₁-C₂₀ alkyl, isoalkyl, cycloalkyl oraryl radical, z is an integer of from 2 to 3 and X is halogen. 27.Catalyst according to claim 26 in which the cocatalyst is selected fromtriethylaluminum (TEAL), triisobutylaluminum, tri-n-butylaluminum,tri-n-hexylaluminum, tri-n-octylaluminum ortris(2,4,4-trimethyl-pentyl)aluminum.
 28. Catalyst according to claim 25in which the external electron donor compound is selected from siliconcompounds of formula R⁵ _(a)R⁶ _(b)Si(OR⁷)_(c), where a and b areintegers of from 0 to 2, c is an integer of from 1 to 3 and the sum(a+b+c) is 4; R⁵, R⁶, and R⁷, are alkyl, cycloalkyl or aryl radicalswith 1-18 carbon atoms optionally containing heteroatoms.
 29. Processfor the (co)polymerization of olefins CH₂═CHR, wherein R is hydrogen ora hydrocarbon radical having 1-12 carbon atoms, which is carried out inthe presence of a catalyst comprising a catalyst component comprisingthe product obtained by contacting a Ti compound of formulaTi(OR)_(n−y)X_(y), where R is an alkyl, isoalkyl, cycloalkyl or arylradical having from 1 to 18 carbon atoms, X is a halogen atom, n is thevalence of titanium and y is a number of from 1 to n, with a pre-polymerhaving a porosity (measured with Hg method) higher than 0.3 cc/g andcontaining from 0.5 to 100 g of polymer per g of a solid catalystcomponent, said pre-polymer being obtained by (co)polymerizing an olefinor a diolefin which is (co)polymerizable in the presence of a catalystcomprising the solid catalyst component, the solid catalyst componentcomprising a transition metal compound selected from the groupconsisting of Ti compounds of the formula Ti(OR)_(n−y)X_(y), vanadiumhalides, haloalcoholates and vanadyl halides, and Ti, Zr and Hfcompounds containing at least a π-metal bond, said transition metalcompound being supported on a Mg dihalide having a mean crystallite sizelower than 30 nm.